const options = {
  method: 'GET',
  headers: {'x-spree-api-key': '<api-key>', Authorization: 'Bearer <token>'}
};

fetch('http://{defaultHost}/api/v3/store/orders/{order_id}/returns', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

curl --request GET \
  --url http://{defaultHost}/api/v3/store/orders/{order_id}/returns \
  --header 'Authorization: Bearer <token>' \
  --header 'x-spree-api-key: <api-key>'

{
  "data": [
    {
      "id": "ret_UkLWZg9DAJ",
      "number": "RET1001",
      "status": "requested",
      "order_id": "or_UkLWZg9DAJ",
      "reason_id": null,
      "refund_total": "10.00",
      "display_refund_total": "$10.00",
      "refund_tax_total": "0.00",
      "display_refund_tax_total": "$0.00",
      "approved_at": null,
      "received_at": null,
      "refunded_at": null,
      "canceled_at": null
    }
  ],
  "meta": {
    "page": 1,
    "limit": 25,
    "count": 1,
    "pages": 1,
    "from": 1,
    "to": 1,
    "in": 1,
    "previous": null,
    "next": null
  }
}